Field of the Invention
The current invention relates to a class of propulsive engines known as turbine-based-combined-cycle (TBCC) engines and more particularly to a turbojet combined with a rotary rocket.
Description of the Prior Art
The need for endo-atomospheric, trans-atmospheric, and exo-atomospheric vehicles has created interest in propulsion systems that can operate in, through, and out of the atmosphere. A number of propulsion systems designed to operate in atmosphere have been proposed. Turbine-based-combined-cycle (TBCC) engines, for example, are propulsive engines that have elements of both turbojet engines, which use atmospheric air as the main constituent of their reaction mass, and rocket engines, which carry all of their reaction mass.
An Air Turbo Rocket (ATR) is a type of TBCC engine which combines a conventional solid or liquid propellant rocket-type gas generator with a conventional turbojet in such a way that heated, fuel rich gas from the rocket is used to power the mechanical compression of air from the atmosphere. This fuel rich gas and the compressed air are then mixed and burned in a turbojet-type afterburner. The air-breathing portion of the ATR uses atmospheric oxygen to burn the product of fuel rich combustion by the rocket in a combustion chamber that is analogous to an afterburner in a turbojet engine. An advantage of an ATR is relatively high thrust generation at high speeds, high thrust per unit frontal area, and a compact and lightweight engine configuration. A primary disadvantage of an ATR is its high propellant consumption rate, relative to a turbojet. U.S. Pat. No. 4,096,803 discloses a solid propellant air turbo rocket that can operate in a ramjet mode by jettisoning a solid propellant rocket-driven turbo-compressor.
EP 0403372 B1 discloses a combined turbo-rocket ramjet engine capable of operating in a combined turbo-rocket mode or a ramjet mode. The engine uses turbopumps to pump fuel and oxidizer to a gas generator that drives a compressor for turbo-rocket mode operation or to radial injectors for ramjet mode operation. The engine operates in turbo-rocket mode at low Mach speeds and switches to ramjet mode at high Mach speeds. Although the engine uses stored oxygen as an oxidizer, this engine uses atmospheric oxygen in all operational modes and is therefore not capable of operation outside the atmosphere.
U.S. Pat. No. 5,159,809 discloses a propulsion engine designed to reversibly change from air-breathing, non-air-breathing, and combined modes. The engine comprises a rocket engine having an annular combustion chamber disposed inside the central body and downstream from the air-breathing combustion chamber of a jet engine. The rocket engine has a streamlined central body portion extending the central body of the air-breathing combustion chamber to form a spike that penetrates into the throat of the external nozzle. The combustion chamber of the rocket engine and the associated streamlined central body are integrated in the main nozzle and penetrate into the main nozzle at the throat while being shaped to ensure aerodynamic continuity of the air-breathing stream from the air-breathing combustion chamber being ejected through the main nozzle. Although this engine concept combines a jet engine with a rocket engine, allowing both air-breathing and rocket propulsion modes, no advantage is taken of combining the required turbomachinery of the jet and rocket engines, and thus the concept requires separate turbomachinery assemblies for the jet and rocket engines, which greatly increases complexity and mass of the overall engine.
Rotary rocket engines use the rotation of a combustion chamber, powered by the release of exhaust gases from the combustion chamber, to pump and mix propellants. The rotational force comes from a tangential component of rocket thrust, which is created by canting one or more rocket nozzles in the rotary rocket assembly. U.S. Pat. No. 2,479,829 and U.S. Pat. No. 2,395,114 disclose rotating combustion chambers in which rotation is produced by the passage of exhaust gases through curved nozzles and against vanes. U.S. Pat. No. 6,212,876 discloses a rocket motor with an ultracentrifugal liquid pump driven by a tangential component of the primary thrust from multiple combustion chambers by means of tilted nozzles or vanes. Rotation of combustion chambers and pump enhances both propellant mixing and combustion chamber cooling by the Coriolis-effect and centripetal acceleration. Rotary rockets provide the advantage of eliminating the weight and complexity of separate, non-integrated propellant pumps compared to pump-fed combustion chambers, and the weight of high-pressure propellant tanks when compared to pressure-fed combustion chambers. Because the rocket chambers are integral with the pump elements, rotary rockets also eliminate the need for high-pressure, high-speed rotating seals, which is a very challenging and expensive issue for conventional turbopump-fed rocket engines. One disadvantage of a rotary rocket is that there is no rotation at start-up so some means other than rotation must be provided for pumping propellants at engine start. Another disadvantage of rotary rockets is that the rocket chambers are heavier than conventional rocket chambers because they must be designed to withstand the centrifugal forces generated during the rotation of the rocket chambers.
Despite the development of the aforementioned propulsion technologies, high speed endo-atomospheric, trans-atmospheric and exo-atomospheric vehicles powered by TBCC engines have not yet come into widespread use. TBCC engines which are only air-breathing are limited in their maximum flight speeds and altitudes, and cannot fly exo-atmospherically. Alternatively, rocket engines have too high of a propellant-usage rate for long-range endo or trans-atmospheric flights. Thus, there is a continuing need for a new TBCC engine capable of continuously providing propulsion from take-off to landing for endo, trans, and exo-atomospheric flight operations.